Application-specific optimization of echo time in MR pulse sequences for investigating materials with susceptibilities different from that of the background in which they are embedded

Abstract

The echo time in an MR pulse sequence is optimized in accordance with the application desired. Advantageously, the echo time is selected to cause a partial volume signal cancellation from veins as compared with background tissue, and the MR pulse sequence is of a velocity-compensated type. MR data are acquired from gradient echoes. Multiple echoes may be used to extract information (such as volume content and susceptibility) about the material under investigation.

What is claimed is:  
     
       1. A method of collecting MR data from a vein-containing and background tissue-containing region of interest within a living subject, comprising the steps of: 
       conducting an MR study using a velocity-compensated MR pulse sequence in which the echo time is selected to cause a partial volume signal cancellation from veins in the region of interest as compared with the background tissue in the region of interest; and  
       acquiring MR data from gradient echoes produced by the MR study.  
     
     
       2. The method of  claim 1  wherein the MR pulse sequence is a gradient echo pulse sequence. 
     
     
       3. The method of  claim 1  wherein the MR pulse sequence is an echo-planar pulse sequence. 
     
     
       4. The method of  claim 1 , wherein the MR pulse sequence is a two-dimensional pulse sequence. 
     
     
       5. The method of  claim 1 , wherein the MR pulse sequence is a three-dimensional pulse sequence. 
     
     
       6. The method of  claim 1 , wherein the MR pulse sequence is a multi-echo pulse sequence. 
     
     
       7. A method of MR imaging a region of interest containing at least two structures having different magnetic susceptibilities and a background material in which said structures are embedded, comprising the steps of: 
       conducting an MR study of the region of interest using a MR pulse sequence in which the echo time is selected to cause different partial volume signal cancellations from the structures as compared with the background material; and  
       acquiring MR data from gradient echoes produced by the MR study.  
     
     
       8. A method of determining oxygen saturation of a subject's blood in vivo in a region of interest, comprising the steps of: 
       conducting an MR study of said region of interest using a velocity-compensated multi-echo MR pulse sequence;  
       acquiring MR data from gradient echoes produced by the MR study; and  
       determining, from the acquired MR data, the oxygen saturation of the subject's blood in the region of interest utilizing an oscillatory signal loss caused by partial volume signal cancellation.  
     
     
       9. A method of determining venous blood volume in a vein-containing region of interest in a subject in vivo, comprising the steps of: 
       conducting an MR study of said region of interest using a velocity-compensated multi-echo MR pulse sequence;  
       acquiring MR data from gradient echoes produced by the MR study; and  
       determining, from the acquired MR data, the venous blood volume in the region of interest.  
     
     
       10. A method for visualizing, in vivo, tissue-embedded reins and arteries located within a region of interest inside a subject, comprising the steps of: 
       conducting an MR study using a velocity-compensated MR pulse sequence in which the echo time is selected to cause a partial volume signal cancellation from veins in the region of interest as compared with arteries and background tissue in the region of interest;  
       acquiring MR data from gradient echoes produced by the MR study;  
       forming an amplitude image of the region of interest from the MR data;  
       forming a phase image of the region of interest from the MR data; and  
       filtering the amplitude image by operating on it with the phase image and thereby producing a filtered image.  
     
     
       11. The method of  claim 10 , further comprising the step of administering a contrast agent to the subject prior to said acquisition step. 
     
     
       12. The method of  claim 11  wherein the images are used to differentiate between two different states of oxygen saturation or blood volume. 
     
     
       13. The method of  claim 11  in which a minimum intensity projection is used to create a projection image displaying veins and in which a maximum intensity projection is used to display arteries. 
     
     
       14. The method of  claim 10 , wherein the MR pulse sequence is a three-dimensional sequence, and further comprising the step of forming a minimum intensity projection of the filtered image. 
     
     
       15. The method of  claim 10 , wherein the MR pulse sequence is a three-dimensional sequence, and further comprising the step of forming a maximum intensity projection of the filtered image. 
     
     
       16. The method of  claim 10 , wherein the MR study is a multislice study, wherein the MR pulse sequence is a two-dimensional sequence, and further comprising the step of forming a minimum intensity projection of the filtered image. 
     
     
       17. The method of  claim 10 , wherein the MR study is a multislice study, wherein the MR pulse sequence is a two-dimensional sequence, and further comprising the step of forming a maximum intensity projection of the filtered image. 
     
     
       18. The method of  claim 10  wherein the resolution is chosen based on the size of a vessel of interest. 
     
     
       19. A method of MR imaging a region of interest comprising the steps of producing an MR amplitude image of said region, producing an MR phase image of said region, and producing a filtered NR image by operating upon said amplitude image using said phase image. 
     
     
       20. The method of  claim 19 , wherein said region includes veins and arteries, and wherein the method is used to produce an image of said region from which the images of veins have been suppressed. 
     
     
       21. A method for visualizing a region of interest containing at least two structures having different magnetic susceptibilities and a background material in which said structures are embedded, comprising the steps of: 
       conducting an MR study using a velocity-compensated MR pulse sequence in which the echo time is selected to cause a partial volume signal cancellation from one structure as compared with the other structure and background in the region of interest;  
       acquiring MR data from gradient echoes produced by the MR study;  
       forming an amplitude image of the region of interest from the MR data;  
       forming a phase image of the region of interest from the MR data; and  
       filtering the amplitude image by operating on it with the phase image and thereby producing a filtered image.  
     
     
       22. The method of  claim 1 , wherein the MR pulse sequence is a gradient echo pulse sequence. 
     
     
       23. The method of  claim 21 , wherein the MR pulse sequence is an echo-planar pulse sequence. 
     
     
       24. The method of  claim 21 , wherein the MR pulse sequence is a two-dimensional pulse sequence. 
     
     
       25. The method of  claim 21 , wherein the MR pulse sequence is a three-dimensional pulse sequence. 
     
     
       26. The method of  claim 21 , wherein the MR pulse sequence is a multi-echo pulse sequence. 
     
     
       27. A method of determining the susceptibility difference between tissues of interest, comprising the steps of: 
       conducting an MR study of a region of interest using a velocity-compensated multi-echo MR pulse sequence;  
       acquiring MR data from gradient echoes produced by the MR study; and  
       determining, from the acquired MR data, the susceptibility difference between said tissues of interest utilizing an oscillatory signal loss caused by partial volume signal cancellation.  
     
     
       28. A method for visualizing, in vivo, tissue-embedded veins and arteries located within a region of interest inside a subject, comprising the steps of: 
       conducting an MR study using a velocity-compensated MR pulse sequence in which the echo time is selected to cause a partial volume signal cancellation from veins in the region of interest as compared with arteries and background tissue in the region of interest and wherein the resolution is selected based on the size of a vessel of interest; and  
       acquiring MR data from gradient echoes produced by the MR study.  
     
     
       29. The method of  claim 28  in which a minimum intensity projection is used to create a projection image displaying veins and in which a maximum intensity projection is used to display arteries.